Beneficiation of ores

ABSTRACT

A method for the beneficiation of an ore containing titanium and iron oxides to produce a beneficiate containing a reduced proportion of iron oxide, which comprises forming a mixture containing the ore and carbon, the carbon content of such mixture being in the range 20 to 40% by weight, and treating such mixture in a fluidized bed reactor at a temperature in the range 800*1000*C with a treatment gas which comprises 20 to 50% by volume of chlorine and 0 to 10% of oxygen.

United States Patent [191 Robinson et al.

[ BENEFlClATlON OF ORES [75] Inventors: Michael Robinson, Grimsby; HarryBrian Wilson, North Thoresby; David Antony Gray, Grimsby, all of England[73] Assignee: Laporte Industries Limited, London,

England [22] Filed: Jan. 24, 1972 [21] Appl. No.: 220,243

[30] Foreign Application Priority Data Jan. 27, 1971 Great Britain03241/71 [52] US. Cl. 75/1, 423/75 [51] Int. Cl C22b 1/00 [58] Field ofSearch 75/1, 1 T, 112; 423/75, 423/149 [56] References Cited UNITEDSTATES PATENTS l2/l939 Muskat et al. 423/75 Mar. 11, 1975 2,l84,885l2/l939 Muskat et al. 423/75 2,852,362 9/1958 Daubenspeck et al. r. 75/22,933,373 4/l960 Love et a1 75/l Primary E xaminerAnth0ny Skapars [57]ABSTRACT A method for the beneficiation of an ore containing titaniumand iron oxides to produce a beneficiate containing a reduced proportionof iron oxide, which comprises forming a mixture containing the ore andcarbon, the carbon content of such mixture being in the range 20 to 40%by weight, and treating such mix ture in a fluidized bed reactor at atemperature in the range 800-1000C with a treatment gas which comprises20 to 50% by volume of chlorine and O to 10% of oxygen.

10 Claims, 4 Drawing Figures PATENTED NARI 1 I975 sum 1 or z PATENTEUMRI 1 5 SHEET 2 OF 2 BENEFICIATION OF ORES The present invention relatesto the beneficiation of ores and more particularly relates to thebeneficiation of ores which contain titanium and iron values. The mostcommon of such ores is ilmenite which contains titanium and iron oxide.If this ore is to be used in the manufacture of titanium tetrachloride,which is an intermediate in metal or titanium dioxide pigmentproduction, then it is desirable to benftciate the ore and remove atleast a proportion of the iron content whilst substantially not removingany of the titanium content.

Intheory such beneficiation can be effected by controlled chlorinationof the ore under such conditions that the iron content is converted toiron chloride whilst the titanium content is unaffected; Unfortunatelyhowever it is difficult to control the reaction in such a way that thisis achieved without either substantial loss of the titanium content orinsufficient removal of the iron content.

Prior proposals to this end have been made in U.S. Pat. Nos. 2,184,884and 2,184,885 (which correspond to British Pat. Nos. 533,378 and533,379). The essential disclosure in U.S. Pat. No. 2,184,884 is thatusing a chlorine-air mixture as the reactant gas the proportion of ironand titanium removed from the ore depends upon the percentage of carbonin the reactant mass. Although the specification states that up to 20%by weight of carbon may be used, the detailed disclosure of the drawingsmakes it quite clear that more than 15% would be grossly uneconomicowing to high loss of titanium from the ore.

In U.S. Pat. No. 2,184,885, on the other hand, no oxygen is present inthe reactant gas and although a diluent is mentioned in thespecification no details are given as to the proportion of such diluent.Moreover, although the specification states that up to 15% by weight ofcarbon can be used, the detailed disclosure makes it clear that it isuneconomic to use more than about 5% of carbon.

in both these prior proposals control of the selectivity of thechlorination is effected by the control of the carbon content ofthereactant mixture and whilst this may be relatively easy using briquetedcarbon and ore in a shaft furnace as described therein, it is notpractical in other forms of furnace now preferred in the industry e.g.fluidized bed.

We have now discovered that using a fluidized bed reactor and an excessof carbon over that considered practicable in the prior proposals,control can be effected by varying the effective partial pressure of thechlorine. Such a procedure is considerably easier to operate and controlthan the prior proposals and gives satisfactory results.

Thus according to the present invention there is provided a method forthe beneficiation of an ore containing titanium and iron oxides toproduce a beneficiate containing a reduced proportion of iron oxide,which comprises forming a mixture containing the ore and carbon, thecarbon content of such mixture being in the range 20 to 40% by weight,and treating such mixture in a fluidized bed reactor at a temperature inthe range 800-l000C with a treatment gas which comprises 20 to 50% byvolume of chlorine and 0 to by volume of oxygen.

it should be noted that in the present invention it is essential to usea fluidized bed reactor and therefore it is necessary to use a loose andpreferably welldispersed mixture of ore and carbon as the charge to thereactor. It will be noted that the minimum carbon content that wepropose is 20% by weight and is therefore greater than that of the priorproposals. However this carbon content is not critical, provided thatthe content lies within the range specified and variations within thisrange do not materially affect the degree of beneficiation. it shouldfurther be pointed out that this range of carbon contents isconsiderably in excess of that required in the reaction and the productbeneficiate is mixed with free carbon. Subsequently the productbeneficiate will normally be mixed with excess carbon and preferably feddirectly to a conventional fluid bed chlorination system to producetitanium tetrachloride.

The beneficiation reaction is temperature sensitive, but control iseffected by the proportion of chlorine in the reactant gas. Similarlycontrol of this proportion will affect the degree of removal of iron andalso the degree of removal of titanium.

It will be appreciated that, if we neglect the carbon mixed with thebeneficiate, it is possible to operate the process in such a way thatthe beneficiate contains any required proportion of titanium and anyrequired proportion of iron. However for practical purposes it isnecessary that the beneficiate should contain in excess of titaniumdioxide and less than about 5% of iron, the remainder being oxides ofother elements such as metals, silicon or phosphorus. Moreover forefficient operation it is necessary at least of the titanium dioxideoriginally present in the ore should be present in the beneficiate. Thusit will be understood that it is uneconomic to produce a beneficiatewhich contains, for example, in excess of 99% titanium dioxide and noiron, if the recovery of titanium dioxide is, for example, only 50% ofthat originally present in the ore.

Considered as an overall process including heat losses from the system,the reaction of chlorine with titanium ores is endothermic which meansthat heat must be supplied to keep the reaction going. As is well knownthis heat can be supplied from external sources either by direct heatingof the reactor vessel or by-preheating of the reactant gas or charge,However, the preferred method of providing the necessary heat is bycontrolled reaction of the carbon content of the charge with oxygen. Inaccordance with the invention up to 10% by volume of the treatment gascan be oxygen and depending upon the other conditions this may or maynot be sufficient to maintain the reaction as thermally self-sustaining.If this proportion of oxygen is insufficient, then additional oxygen maybe injected into the reactor but this must be done at such a locationand in such a way that the products of the reaction when mixed with thetreatment gas do not take the total reactant gas composition outside thelimits specified.

Thus according to a further feature of the invention, the processcomprises separately injecting a heating gas into the reactor at alocation below the point of injection of the treatment gas, such heatinggas containing a proportion of oxygen such that the process is thermallyself-sustaining and the point of injection being such that at the levelof injection of the treatment gas the oxygen content of the combined gasflows is less than 10% by volume.

As has been indicated above it is necessary to overcome theendothermicity of the overall selective chlori- 3 nation reaction bysupplying heat to the system. In order to minimize the amount of heatrequired to be added, several factors can be manipulated. Thus thereactor vessel may be located withina furnace and may be preheated bymeans of this furnace before passing any reactant gas into the systemand it of course follows that the charge within the reactor vesselwill'be preheated at the same time. A convenient temperature to whichthe reactor vessel is preheated is within the range from 850 to 950C andany further solid material supplied to the reactor vessel mayconveniently be preheated to this temperature. It may also be desirableto preheat the reactant gases. The diluent gas is conveniently chosen sothat it has a low specific heat and in consequence we prefer to usenitrogen rich mixtures rather than carbon dioxide rich mixtures as maybe obtained for example from the recycle of exhaust gases produced inthe reactor vessel. The volume of diluent gas required will of coursedepend on the desired partial pressure of chlorine but obviously thehigher the proportion of chlorine the lower the proportion of diluentgas required and consequently the lower the amount of heat which has tobe supplied to the diluent gas. The invention is particularly suited tothe preferred range of 30 to 45% by volume of chlorine within thetreatment gas.

To assist in heat economy it is convenient to preheat the treatment gasby extracting the heat from the solid product i,e. beneficiate cokemixture as by means of a counter current exchanger or contacting device.The fresh charge is conveniently pre-heated in a fluid bed contactingdevice in which some of the coke is combusted using air, additional cokebeing added to the feed for this purpose. It will be apparent that theneed for heat economy is particularly important when a continuousprocess is being used.

The quantitative chemical reactions which take place in the reactorvessel are not known but although we do not wish to limit our inventionby discussing what we believe to be the theory of reaction, we believethat the selectivity of attack affording preferential attack on the ironcontent of the ore is basically due to the fact that chlorination ofiron values results in an increase in the volume of gaseous componentswhilst chlorination of titanium dioxide does not result in any increasein volume.

We have found, experimentally, that the relative proportions of ferrouschloride and ferric chloride depend upon the relative amount of gaseouschlorine and iron in the bed. We prefer to operate in such a way thatthe predominant product is ferrous chloride which, since it is volatileat the reaction temperature employed, is rapidly car'ried away from thesystem by the outlet gases. This lower chloride of iron is surprisinglyobtained without prior reduction of the ore by using chlorine diluted tothe extent specified herein. It will be appreciated that when thepredominant product is ferrous chloride then the chlorine content ofthe'outlet gases will be small and perhaps undetectably small. Indeedone of the major advantages of operating so that ferrous chloride is thepredominant product is the saving in the amount chlorine used.

The amount of oxygen in the reactant gases is normally controlled to besufficient to ensure that the oxides of carbon are present mainly ascarbon dioxide which is a preferable effluent gas to carbon monoxide 4and which moreover makes maximum use of the carbon content of the chargefor generating heat.

In order that the present invention may be more readily understood thesame will now be described by way of example and with reference to theaccompanying drawings wherein FIG. 1 is a diagrammatic representation ofa first embodiment of reactor vessel,

FIG. 2 is a diagrammatic representation of a second embodiment ofreactor vessel,

FIG. 3 is a graph showing TiO recovery plotted against chlorine contentand FIG. 4 is a graph showing iron content of beneficiate as againstchlorine content.

Referring now to the drawings and to FIG. 1 in particular the reactantvessel 10 comprises a generally cylindrical body having walls 11 made ofa material which is resistant to heat and to chlorine such as, forexample, fused silica. The reactor vessel 10 is located in a furnace(not shown). The base of the reactor vessel is closed by a perforatedbase plate 12 below which is a plenum chamber 13 with a gas inlet 14 forthe treatment gas. A gas off-take 15 is provided near the top of thevessel. An inlet 16 is provided near the top of the reactor vessel 10for the charge of ore and coke andan outlet 17 is provided near the baseof the vessel for the product beneficiate.

Very conveniently the charge comprises by weight of ilmenite ore forexample West Australian ilmenite which analyzes at 54.5% TiO and 30% Fepresent as oxides together with 25% by weight of coke. Fludization ofthe bed of coke and ore, the components of the charge, is possiblewithout grinding the mixture, the ore being in its natural size range of-l80u.

In use the charge is placed in the reactor vessel and is fluidized by aflow of nitrogen or other inert gases whilst the reactor vessel andcharge are heated to a temperature of approximately 900C by means of thesaid furnace. When the reactor and its contents have reached thetemperature of 900C the fluidizing gas is replaced by a treatment gascomprising 42% by volume of chlorine and 10% by volume of oxygen, theremainder being nitrogen and other inert gases. It is found that a timeof between two and three hours is necessary for substantially completereaction and at the end of this time the chlorine and oxygen feed areswitched off and the bed cooled whilst the flow of inert gas wasmaintained. At the end of the cooling period the bed contents wereanalyzed as comprising coke with beneficiate of composition 92.7% byweight TiO and 1.4% Fe O The recovery of TiO was 96%. When the unit isoperated continuously the ore and coke mixture is continuously addedthrough a feeding device located at the inlet 16 and the beneficiatedore is withdrawn at frequent intervals through the outlet 17 with theexcess coke. I

This apparatus may easily be adapted to function continuously by usingas the initial bed a mixture of 80% by weight beneficiate and 20% byweight coke in which the beneficiate analyzes at 93.5% by weight oftitanium dioxide. At 900C chlorine is admitted at the base of thereactor to give a 40% v/v concentration on the inert fluidizing gasstream while ilmenite ore and coke in the ratio of 80% to 20% by weightresepectively are continuously fed into the system. As shown'in Table Iit can be seen that the beneficiate recovered from outlet 17 over aperiod of 4 hours has a high titanium diox- Table I Time (hours) %(byweight) of TiO in recovered beneficiate bum-.

In this steady operation no chlorine was detected in the efflux gasesand analyses of samples of it showed that substantially all the ironchloride was ferrous chloride.

It should be remarked that the ore contains a certain measure ofimpurities some of which will be removed during this chlorinationprocess but some of which will go through to the beneficiate. It isnecessary for economical working to get a recovery of better than 95% ofTiO that is to say not more than of the TiO should escape throught thegas outlet. For satisfactory working the beneficiate should analyze atbetter than 90% TiO or seen from another point of view should containless than about 5% of Fe O It was found using the apparatus of FIG. 1that it was difficult to obtain a satisfactory thermal balance withoutintroducing an excessive amount of oxygen. The apparatus of FIG. 2 wastherefore devised.

In the apparatus of FIG. 2 the reactor vessel is again of generallycylindrical form and is made of fused silica. It comprises an uppersection 21 and a lower section 22 of smaller diameter than the portion21. The base of the section 22 is provided with a perforated base plate23 and a gas plenum chamber 24 with an inlet 25 for gases. At thejunction between the portions 21 and 22 there is a generally annularportion 26 provided with a plurality of gas inlets 27.

The reactor vessel 20 is also provided with a gas offtake 28 and inlet29 for the charge and an outlet 30 for the beneficiate. As before thereactor vessel is located in a furnace.

In one experiment using the apparatus of FIG. 2, a charge of 65 lbs ofWest Australian ilmenite was placed in the vessel together withapproximately 22 lbs of coke. The reactor vessel was heated up to 900Cin the furnace using a fluidizing flow of nitrogen and when it reachedthis temperature oxygen was admitted through the gas inlet 25 to theextent of 20% by volume of the fluidizing gas. This flow of oxygen wascalculated to provide a steady temperature and at least 50% of theoxygen was consumed before reaching the upper section 21 of the reactorvessel. Chlorine was admitted through the gas inlet 27 to the extent of28% by volume of the total gas flow. After a sufficient reaction period(approximately 2 hours l0 minutes) the chlorine and oxygen flows werestopped and the bed contents cooled and recovered. The beneficiateanalyzed at 94.1% Ti0 and 1% Fe O with the recovery of TiO being inexcess of 95%.

In order to demonstrate the criticality of the chlorine content of thetreatment gas a series of experiments were carried out at-various volumepercentages of chlorine and the results are plotted in FIGS. 3 and 4. Inboth FIGS. 3 and 4 the minimum recovery of Ti0 was 95% by weight, thisbeing the minimum recovery which is economically satisfactory. It isseen quite clearly in FIG. 3 that the purity of the beneficiate remainsbetter than TiO up to about 45% by volume of chlorine in the treatmentgas. The reason for the sudden fall in purity of the beneficiate isclearly apparent from FIG. 4 where up to slightly more than 45% byvolume of chlorine in the treatment gas gives an iron content of lessthan 4% but with the iron content increasing rapidly with higherpercentages of chlorine in the treatment gas.

It will be apparent that in all cases and in contrast to the priorproposals hereinbefore mentioned, the charge to the reactor vesselcontains in excess of 20% by weight of carbon and it is also clear thatunder the conditions of this invention the critical factor is thechlorine concentration in the treatment gas and not the carbon contentof the charge. It should however be emphasised again that the carboncontent must be in excess of that necessary for the reaction. Thebeneficiate is therefore mixed with carbon.

It will be appreciated that control of the chlorine content of thetreatment gas is readily effected by controlling the amount of chlorineand/or oxygen and for diluent gases fed to the reactor. The effect ofthe control can be measured by monitoring the off gases for chlorine,ferrous/ferric chloride titanium tetrachloride and carbon oxides. Itwill be apparent that control of the reaction is much easier and moreeffective than by control of the carbon content.

We claim:

1. In a method for the beneficiation of an ore con taining titaniumdioxide and a mixture of iron oxides to produce a beneficiate containinga reduced proportion of iron oxides, wherein the improvement comprisesforming a mixture of the ore containing the said mixture of iron oxidesand carbon, the carbon content of the mixture being in the range of from20 to 40% by weight and said carbon content being in excess of thatnecessary for reaction, enclosing the mixture in a fluidized bedreactor, treating the mixture in a fluidized bed reactor at atemperature in the range of 800 to 1,000C. with a treatment gasessentially consisting of 20 to 50% by volume of chlorine, 0 to 10% byvolume of oxygen and a diluent gas whereby control of the beneficiationreaction is effected by the proportion of chlorine in the reactant gas,and recovering the resulting beneficiate from the reactor.

2. A method according to claim 1 which includes separately injecting aheating gas into the reactor at a location below the point of injectionof the treatment gas, such heating gas containing a proportion of oxygensuch that the process is self-sustaining and the point of injectionbeing such that at the level of injection of the treatment gas theoxygen content of the combined gas flows is less than 10% by volume.

3. A method as claimed in claim 1 in which the reactor is located in afurnace.

4. A method as claimed in claim 1 in which the reactor is pre-heated toa temperature in the range from 850 to 950C.

5. A method as claimed in claim 1 in which the treatment gas includesnitrogen.

6. A method as claimed in claim 1 in which the treatment gas comprises30 to 45% by volume of chlorine.

7. A method as claimed in claim 1 in which the ferrous chloride isproduced.

8. A method as claimed in claim 1 in which substantially no chlorine isdetectable in the outlet gases.

9. A method as claimed in claim 1 wherein the fluidized bed reactor isoperated continuously.

10. A method as claimed in claim 1 wherein the diluent gas is a nitrogenrich mixture.

1. IN A METHOD FOR THE BENEFICATION OF AN ORE CONTAINING TITANIUMDIOXIDE AND A MIXTURE OF IRON OXIDES TO PRODUCE A BENEFICATE CONTAININGA REDUCED PROPORTION OF IRON OXIDES, WHEREIN THE IMPROVEMENT COMPRISESFORMING A MIXTURE OF THE ORE CONTAINING THE SAID MIXTURE OF IRON OXIDESAND CARBON, THE CARBON CONTENT OF THE MIXTURE BEING IN THE RANGE OF FROM20 TO 40% BY WEIGHT AND SAID CARBON CONTENT BEING IN EXCESS OF THATNECESSARY FOR REACTION, ENCLOSING THE MIXTURE IN A FLUIDIZED BED RECTOR,TREATING THE MIXTURE IN A FLUIDIZED BED REACTOR AT A TEMPERATURE IN THERANGE OF 800* TO 1,000*C. WITH A TREATING GAS ESSENTIALLY CONSISTING OF20 T0 50% BY VOLUME OF CHLORINE, 0 TO 10% BY VOLUME OF OXYGEN AND ASILUENT GAS WHEREBY CONTROL OF THE BENEFICATION REACTION IS EFFECTED BYTHE PROPORTION OF CHLORINE IN THE REACTANT GAS, AND RECOVERING THERESULTING BENEFICATE FROM THE REACTOR.
 1. In a method for thebeneficiation of an ore containing titanium dioxide and a mixture ofiron oxides to produce a beneficiate containing a reduced proportion ofiron oxides, wherein the improvement comprises forming a mixture of theore containing the said mixture of iron oxides and carbon, the carboncontent of the mixture being in the range of from 20 to 40% by weightand said carbon content being in excess of that necessary for reaction,enclosing the mixture in a fluidized bed reactor, treating the mixturein a fluidized bed reactor at a temperature in the range of 800* to1,000*C. with a treatment gas essentially consisting of 20 to 50% byvolume of chlorine, 0 to 10% by volume of oxygen and a diluent gaswhereby control of the beneficiation reaction is effected by theproportion of chlorine in the reactant gas, and recovering the resultingbeneficiate from the reactor.
 2. A method according to claim 1 whichincludes separately injecting a heating gas into the reactor at alocation below the point of injection of the treatment gas, such heatinggas containing a proportion of oxygen such that the process isself-sustaining and the point of injection being such that at the levelof injection of the treatment gas the oxygen content of the combined gasflows is less than 10% by volume.
 3. A method as claimed in claim 1 inwhich the reactor is located in a furnace.
 4. A method as claimed inclaim 1 in which the reactor is pre-heated to a temperature in the rangefrom 850* to 950*C.
 5. A method as claimed in claim 1 in which thetreatment gas includes nitrogen.
 6. A method as claimed in claim 1 inwhich the treatment gas comprises 30 to 45% by volume of chlorine.
 7. Amethod as claimed in claim 1 in which the ferrous chloride is produced.8. A method as claimed in claim 1 in which substantially no chlorine isdetectable in the outlet gases.
 9. A method as claimed in claim 1wherein the fluidized bed reactor is operated continuously.